In reeling or winding of paper or other, equivalent web-like material, in the forming of machine reels, a so-called Pope-type reel-up is commonly employed. In a Pope-type reel-up, the paper reel is formed by loading the reel against a Pope drum.
On the other hand, in slitter-winders, in which customer rolls are formed, winders of the drum winder type are commonly used. In a drum winder, there are two winding drums, on whose support the paper roll is formed. The paper roll that is being formed is loaded by means of rider rolls which are brought into contact with the top face of the paper roll. From the drum winder, a winder with a set of belt rolls has been developed further, in which one of the winding drums has been substituted for by two smaller rolls which are surrounded by an endless carrier belt that supports the paper roll. In slitter winders, a center-drive winder is also employed, in which the roll is formed on support of one winding drum so that the roll is constantly supported from its center by means of an adjustable hydraulic support.
When a paper web or equivalent is reeled or wound, it is the primary objective that the web that is formed should be reeled or wound onto the reel or roll as evenly as possible in order that the reel or roll should have a uniform quality in view of enabling and improving further processing. In order that this objective could be achieved, a number of different methods and apparatus have been suggested for controlling the reeling or winding process. In practice, the reeling or winding process can, however, not be controlled completely and in reeling or winding, defects unavoidably arise in some reels or rolls. Since such defects cause problems in the subsequent processing of the reeled or wound material, it would be advantageous if the defective reel or roll, the location of the defect in the reel or roll, and the nature of the defect could be identified right in the stage of reeling or winding.
Predicting a deficiency in the structure arising from reeling or winding and the presence of damage arising from this deficiency in the web is, however, not reliably possible today. For this reason, if it is suspected that, for example, in a line of paper manufacture, in a machine reel, there is bottom damage or other damage, in the unwinding taking place in the next process stage, a sufficiently large bottom portion is allowed to remain so as to be on the safe side. Since bottom damage that results in web breaks generally does not occur systematically in every machine reel, as a result of such a procedure, unnecessary broke, and thus also unnecessary economic losses, arise. Similarly, web damage in customer rolls causes web breaks in the printing machine, which is an undesirable situation from the point of view of the printing operator, because it lowers the efficiency of the printing machine.
Methods of NDT (Non-destructive testing) of machine reels and rolls in general have not been developed very actively, in spite of the necessity of availability of such methods. Research has been carried out, among other things, into tomography and into thermographic analysis. Experiments have provided promising results, but the methods still require a large amount of further development before they are able to be utilized for predicting structural defects in a reel or roll. In particular, for analysis of a machine reel, there are not sufficiently large tomographic apparatus, and the cost would probably constitute an obstacle for development of such apparatus. Thermography is restrictive in the sense that the examination is carried out by depicting the surface or the end of the reel or roll. In such a case, the results are based on observation of the difference in temperature arising from movements between layers of paper and produced by friction heat, which does not state very precisely where and what sorts of reeling or winding defects have arisen. Further, the stability of the emission coefficient of the paper, for example, in situations of pressing, is not known.
With respect to thermographic analysis, reference is made to International Publication No. WO 95/27676, in which a method is described by whose means the higher temperature of a defective point in a reel or roll is measured by means of a thermograph. Thus, thermal radiation is measured here. Thermal radiation, i.e., infrared radiation, is electromagnetic radiation, which is transmitted by every object whose temperature is above the absolute zero point. Thermal rays move at the speed of light. The intensity of the radiation depends on the temperature of the object and on the wave length of the radiation. With the exception of a fully black object, every object also reflects and absorbs radiation coming from other sources. Defects in a reeling or winding process are converted to heat, for example, by the effect of friction, which slows down, equalizes and weakens the interdependence between the impulse and the signal and thus, makes the method deficient.
When a customer roll or a machine reel becomes larger, in the reeling or winding situation various bangs and creaks are often heard, which arise from relative movements of layers of paper in the roll or reel. These sounds are also observed in situations of braking and acceleration of a roll or reel. The human ear cannot detect from where the sounds arise and what is more precisely taking place in the interior of the roll or reel. Sounds arising from life in the reel are indicative of changes taking place in the structure of the machine reel. Sounds in a certain frequency range indicate the formation of a detrimental reeling or winding defect.